Biosensors are the devices that find application in almost every field nowadays. In this paper, GaN MOSHEMT based biosensor is proposed for detection of biomolecules such as ChOx, protein, streptavidin and Uricase. The effect of biomolecule species on the performance parameters of the device has been studied. It has been observed that there is a significant increase in the drain current and gd is observed with the addition of biomolecule in the nanocavity. The electron concentration contour is studied which shows the rise of carrier concentration with biomolecule. Maximum positive shift is observed in threshold voltage for Uricase due to lowest dielectric constant. Similarly, the change in transconductance is also obtained with biomolecules. The effect of cavity dimensions on sensitivity is also studied. The maximum increase of 10% in channel potential is noted due biomolecule presence in the cavity. This device has shown good sensing and can be used for biosensing applications efficiently in addition to the high power performance of MOS-HEMTs.