Herein, a heterojunction AlGaAs/GaAs PIN diode material structure for a millimeter wave switch and limiter applications is designed, and the two main factors (i.e., the Al doping concentration and I-layer thickness) that influence the performance of the diode are analyzed and optimized. Furthermore, the verification device is fabricated via molecular beam epitaxy and semiconductor process flow sheet technique. We test the device, and the test results show that the opening voltage of the PIN diode is 1.06 V, and the breakdown voltage is 26. The insertion loss of the diode is approximately 1 dB and the isolation degree is 12 dB (when the frequency is 30 GHz), both of which are observed in the frequency range of 1-40 GHz. Thus, the designed device is suitable for millimeter wave switch and limiter circuits.