Unlike SiC unipolar devices, the on-state resistance of diamond unipolar devices based on bulk conduction has a negative temperature coefficient (NTC) which reduces the conduction losses at high junction temperatures. Thus, in order to associate these opposed temperature coefficients, the current article focuses on the modeling of an hybrid power device composed of a n-type 4H-SiC MOSFET and a p-type diamond bulk FET device. The optimal performances and sizing of SiC and diamond devices are introduced and calculated, as an initial benchmark under the same specifications. Based on an analytical modeling of both switching and conduction losses, junction temperatures and associated heatsink paremeters, the hybrid device performances are evaluated for a synchronous buck converter operating at 1200V-1A and at an ambient temperature of 300K. The results described in the manuscript highlight an equilibrium of the hybrid device total losses over a large range of temperatures as well as a reduction by two of the SiC active area. The proposed analysis could be further extended to different voltage/current classes to meet the requirements of alternative applications.