Advanced GaAs MMICs with electrostatic-discharge (ESD) protection devices were developed. The ESD protection devices consist of anti-series connected PIN diodes, which are formed on a wafer with enhancement- and depletion-mode AlGaAs/InGaAs HJFETs. To realize high ESD tolerance, a constant capacitance at low bias, and low harmonics at high frequency, the PIN diodes were optimized in terms of Zenner-like characteristics. As for the GaAs MMICs with ESD protection devices, their survival voltages under a human-body model test are high (i.e., 2000 V). This promising ESD-protection device has been applied to MMIC products such as antenna switches and low-noise amplifiers. This technology has already been implemented in our mass-production processes for fabricating high-performance MMICs for “3-G” phones.