The USB-IF offers a Qualification by Similarity program to member companies that allows certain products to be granted USB certification and be placed on the USB-IF Integrators List with little or no testing.   The QbS program enables a new USB peripheral, host or hub that is substantially similar to a fully tested and certified USB product to be granted certification based on its similarity to the originally certified product.   The purpose of the QbS program is to speed time-to-market and to minimize certification costs.   It is not intended to eliminate the requirement that a product actually pass USB-IF compliance tests.

The only authority to grant Qualification by Similarity to a product is the USB-IF.   No test facility or any other entity is authorized to grant or pursue Qualification by Similarity requests on behalf of the USB-IF.   The qualifying product must be similar to a USB certified product that has undergone full and complete compliance testing.   The qualifying product cannot be compared to another product that itself has been granted Qualification by Similarity.   The certified product, otherwise known as the parent product in a QbS submission, cannot be older than 2 years old. Exceptions are made for host silicon, hub silicon and automotive specific hubs and embedded hosts, which have an age restriction of 3 years.

NOTE:  Connectors and Cable Assemblies, due to their simplicity, may base the similarity on a product that itself has been granted QbS.  Also, the age of the certification of the base connector or cable assembly is not limited to 3 years.

Modifications to the qualifying product are not allowed after submitting a Qualification by Similarity Request to the USB-IF.

Below is a general description of the Qualification By Similarity process:

  1. Member companies submit a Qualification by Similarity request using the form available at
  2. If applicable, the USB-IF will request specification sheets/drawings of both the originally certified and new products.
  3. A review of the QbS request and specification sheets/drawings will be performed by the USB-IF.   One or more of the authorized test labs and/or other USB-IF member experts in a given field may be consulted.
  4. The USB-IF will issue its assessment to the vendor. One of three outcomes is possible:
  5. If the assessment requires passing a subset of compliance tests, the vendor will be informed of the required tests in an email from the USB-IF that includes a QbSID number
  6. The vendor has 90 days to submit the product for testing to the authorized test lab of their choice along with a copy of the email
  7. The test lab should request a copy of the specification drawings from the USB-IF to verify that the product submitted for testing matches the drawings.   Please use the QbSID number when requesting the drawings.
  8. The authorized test lab performs only the tests identified in the email
  9. Upon successful completion of the tests, the authorized test lab will send an email to along with the test results and the ReplyID number.
  10. If the product passes all required tests, then the USB-IF will grant Qualification by Similarity to the product, issue a TID number and add the product to the Integrators List.

    NOTE:  Should the qualifying product fail any required compliance test, the authorized test lab must immediately notify the USB-IF of the failure where the product is automatically denied certification and becomes ineligible for the Qualification by Similarity program.   In order to obtain certification, the qualifying product will have to satisfactorily complete the entire compliance test program for its category.   In addition, the USB-IF may require the base (certified) product undergo a certification audit at the vendor’s expense.

Requirements for Retest

The qualifying product must be derived directly from the certified product with only minor changes.   If any changes are made that would create "significant differences" between the certified product and the qualifying product then retesting is required.  The definition of "significant differences" is sometimes debatable and the final judgment is the responsibility of the compliance review board which reports to the USB-IF Board of Directors. 

Notable decisions on what is considered a "significant difference" will be listed here.  The following guidelines posted below are not comprehensive.  The ultimate responsibility for making sure that production product matches the product samples submitted for compliance testing lies with each vendor.  Audits by USB-IF that reveal discrepancies between shipping product and samples tested may be cause for required re-test, revocation of certification, and/or legal action.

It is recommended that the most full featured and power demanding version of a product be tested for USB certification.  Removing features, functions and depopulating components are more likely to be granted QbS than otherwise.

Signficant Difference Guidelines

Devices (Peripherals, Hosts, Hubs, Embedded Hosts, etc.)

Retest Typically Not Required
  • Aesthetic changes to the product's housing (such as color)
  • Changes to the product's packaging (color, shape, etc.)
  • Microcontroller firmware change (changes in fully modular code not associated with USB functions)
  • Microcontroller change to another certified microcontroller (no PCB layout change, no firmware change)
  • USB connector change to another certified connector (no PCB layout change)
  • Removal of modular features (no PCB changes)
Retest Typically Required
  • Any change to the PCB where USB circuitry resides (trace widths, trace layout, components added, etc.)
  • Addition of USB functions

Retest Typically Not Required
  • Removal of features via bond options or fuse options
  • Package change within the same package family
Retest Typically Required
  • Metal steppings
  • Die changes
  • Package family change
Note: Chipset Design Changes.

Chipsets are modular in nature and changes in one module are unlikely to affect the IP in a different module. Changes to chipsets that are unrelated to USB still require testing, but the tests are limited to validating signal quality of USB. There is no need to validate protocol timings related to packets.


Retest Typically Not Required
  • Color change of thermoplastics 
  • Terminations increase in length
  • Addition/Removal of locator pegs
Retest Typically Required
Cable Assemblies

Retest Typically Not Required
Retest Typically Required


     VTM Engineering and Technical Services Group