PSID has collected information about college major (field of study) in all waves since 2013. Because college majors can be unique and therefore potentially identifying, PSID provides information about full college major only under restricted contract.

As of the PSID-2019 we have recoded all college majors reported in prior waves and pulled the information forward to the current wave, using the new code frame provided by NCES: Classification of Instructional Programs (CIP 2010 frame). Given the granularity of the code frame, we have provided two variables for each college major mention.
  The first variable is the first 2 digits of the CIP which is the main category (e.g., 01=Agriculture, Agricultural Operations, and Related Sciences). The 2-digit version of these variables is publicly available. The second corresponding variable for each mention is the full CIP code, in the format XX.XXXX, is suppressed and only available for use under a restricted data use contract. Users should note that these College variables have character values to preserve the leading zeros to match the CIP 2010 frame. The College Major Family-level and Individual-level codebooks describes the restricted variables.