We build upon our previous work on 4H SiC lateral MOSFETs to present physics based numerical modeling and characterization of a 4H-SiC DMOSFET operating in ON state. Comparison of simulated ON state characteristics to experiment shows that surface roughness scattering dominates at the operating bias of VGS=15V, whereas interface trap density contributes to reducing the inversion charge in the channel and thereby increasing the ON resistance. OFF state performance of the DMOSFET was modeled by considering impact ionization in the device. Excellent leakage characteristics were observed with the device blocking 2kV drain voltage. Impact ionization related breakdown was observed at 2048V drain bias.