Abstract: A tunable diode laser absorption sensor was developed to measure gas temperature, which exploited scanned-wavelength direct absorption spectroscopy and fixed-wavelength modulation spectroscopy with second harmonic detection on two water vapour spectral features near 7 454.4 cm-1 and 7 185.6 cm-1. The sensor was capable of making absolute measurement and could reach 10 kHz output bandwidth using fixed-wavelength modulation spectroscopy. Its performance and accuracy were validated and demonstrated in a static cell with known temperature and pressure. The measured temperature using two techniques agree to within 2% RMS of thermocouple reading for temperature from 600 to 1 000 K, which indicates the sensor is capable of making rapid and highly accurate temperature measurement for uniform flow.