In order to be identified as a "certified" specialist in California, an attorney must be certified either by The State Bar of California Board of Legal Specialization or an organization whose certification program has been accredited by The State Bar of California. (Such an organization must have requirements for certification that are at least equal to those of The State Bar of California's program.)

California attorneys certified as specialists must:
1. Pass a written examination in their specialty field.
2. Demonstrate a high level of experience in the specialty field.
3. Fulfill ongoing education requirements.
4. Be favorably evaluated by other attorneys and judges familiar with their work.
http://ls.calbar.ca.gov/

Certification as a Criminal Law Specialist
http://rules.calbar.ca.gov/LinkClick.aspx?fileticket=76U8m-K-irs%3d&tabid=1149
To be certified as a criminal law specialist, there is a task requirement, an educational requirement, and an independent inquiry into each applicant.