The bias dependence of is addressed in (4.5). The three contributions to can be evaluated by device simulation. The contribution and are independent of the bias. They can be reduced by the gate geometry, see , to reduce the fringe parts or by low-k dielectrics. is a decreasing function of . The value of saturates for high , as can best be seen for a doping concentration of = 110 cm in Fig. 7.12. Next to the bias, the value of the semiconductor contribution strongly depends on the cap concentration. Thus, for high-power HEMTs with depleted caps this contribution reduces to very small values of the contribution of .