Laser interferometric spectra and plasma emission spectra are widely used to realize precise dry etching depth control of compound semiconductor devices. However, fixed wavelength light sources for the laser interferometric systems are limited to analyze end point detection signals. Our ICP dry etching systems such as the RIE-400iP, and RIE-800iP are equipped with a highperformance in-situ monitoring system that can analyze multiple wavelengths from the reflected light of Xe or Xe-Hg (or Halogen lamp). The system is also capable of detecting the variation of plasma emission intensity simultaneously. In this work, we present examples of applying the high-performance in-situ monitoring system to GaAs, InP, and GaN-based device structure etching, and discuss the possibility of highly accurate and stable etching depth control.