Empirical expressions for the composition and temperature dependence of intrinsic carrier densities in Si1-xGex, In1-xGaxAs and In1-xGaxAsyP1-y are developed. The value is then used to compute the minimum capacitance in AlSi3N4Si1-xGex MIS structures and good agreement is obtained with the experimental data. The expected values of minium capacitance for MIS diodes made of the other two materials are given. © 1993.