We apply a collisional semikinetic model to the study of the topside ionosphere transition region. In this study we consider the transition from (1) O+ to H+ dominance, (2) subsonic to supersonic H+ flow, and (3) collisional to collisionless plasma. We focus primarily on the H+ ions as they flow upward from a relatively low altitude of 500-1000 km to a high altitude of 7000 km. These ions are subjected to collisions with O+ ions and self collisions, as well as the effects of macroscopic forces such as the magnetic mirror force, gravity, and the ambipolar electric force. We find that when supersonic outflow occurs, the H+ velocity distribution function shows a large departure from Maxwellian with a large positive and then negative heat flow, particularly in the region where the flow Mach number passes through one. In cases where subsonic outflow occurs and the H+ density is relatively low, distribution functions with two peaks can occur. In these situations the H+ ions have large parallel temperatures and large heat flows when the two peaks are of unequal height. ¿ American Geophysical Union 1992