We report the first monolithic integration of InGaAs/InAlAs resonant tunneling diode (RTD) and high electron mobility transistor (HEMT) epitaxially grown on an InP substrate. The transconductance for a 1-µm gate HEMT was 430 mS/mm and the peak-to-valley current ratio of the RTD was 5.1. Using the integrated structure, we demonstrate basic digital circuits to show low power characteristics of an RTD-load inverter and a static RAM cell circuit, consisting of a single transistor with two RTDs on the transistor. The memory cell circuit exhibits bistability, based on the RTD's negative differential resistance (NDR), at supply voltages from 0.6 to 1.1 V. The static power consumption was 7.3 µW/gate for the inverter and 3.0 µW for memory cell.