We investigate the performance of a 25 Gbaud 850 nm vertical-cavity surface-emitting laser (VCSEL) with reduced temperature dependence from −40 to 125 °C. The VCSEL design implements chirped quantum wells (QWs) with different compositions to broaden the gain spectrum and achieve sufficient performance over the entire temperature range at constant bias current and modulation voltage. A 6μm oxide aperture diameter VCSEL supports data transmission at 25 Gb/s NRZ from −40 to 125 °C with 8 mA bias current and 640 mV modulation voltage. The temperature dependencies of basic performance parameters are also compared to those of a conventional VCSEL with identical QWs.