Green’s Dictionary of Slang

partly, to some extent.

1965		H. Williamson Hustler 7: I’d expected to do somethin’, not to kill him but to hurt him! I meant to do somethin’ to him kind a semi what he had did to me! [Ibid.] 77: One of these guys, I had knew him slightly. He was livin’ semi in my neighborhood.
1972		D. Jenkins Semi-Tough 95: That place we were at [...], was what you might call semi-O.K.