A unified analysis of the current and conductance in metal‐insulator‐degenerate semiconductor tunnel junctions has been made by taking into account the nonparabolic momentum in the insulator. The current may either increase monotonically with voltages or exhibit a maximum at a voltage less than the Fermi energy of the semiconductor. For the conductance, a minimum always occurs at a voltage equal to or less than the Fermi energy and an additional pair of extrema may exist. The criteria for the various cases are established in terms of a set of reduced parameters of the junction. The effect of nonequal electron masses in the semiconductor and the insulator is also considered and shown to be important in determining the different shapes of the characteristics.