The High Altitude Monolithic Microwave Integrated Circuit (MMIC) Sounding Radiometer (HAMSR) is a 25-channel cross-track microwave sounder that uses Monolithic Microwave Integrated Circuit (MMIC) technology to reduce the size and mass of the instrument while improving the instrument's measurement sensitivity and accuracy. The instrument operates at microwave frequencies that can penetrate clouds, enabling it to determine temperature, humidity, and cloud structure under all weather conditions. HAMSR measurements can be used to infer the 3D distribution of temperature, water vapor, and cloud liquid water in the atmosphere, even in the presence of clouds.