Here is a quick queer word for the week.

성별정체성 (seong-byeol-jeong-chae-seong)

성별 is your sex. For example:

등록 카드에 성별을 기입해 주십시오 (Please enter your sex on the registration card).

정체 is your identity. 정체를 드러내다 (To reveal one's true self).

Source

So your 성별정체성 is your gender identity. Pretty simple!