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AlGaInAs-MQW distributed reflector (DR) laser with semi-insulating buried-heterostructure (SI-BH) has been developed as a high speed light source for short reach data transmissions. The DR laser has DBR mirrors on both sides of a DFB active region. Owing to the increased optical feedback with these DBR mirrors, we can obtain short-cavity lasers without increasing threshold gain. The small active region of the DR laser, which comes from the combination of the short cavity structure and the SI-BH waveguide, makes driving current lower. The fabricated DR lasers have shown excellent characteristics such as stable single mode operation, and high values of relaxation oscillation frequencies under low driving current in a wide temperature range. We have achieved 25- and 40-Gbps direct modulation with low driving current. Using four different wavelength DR lasers, whose lasing wavelengths coincide with LAN-WDM grid, 25.8- Gbps direct modulations with sufficient mask margins was obtained. Using 1.55-m-wavelength DR lasers, we achieved 40-Gbps direct modulation with 5 dB dynamic extinction ratio with the driving current less than 50 mA even at 85°C. 40-Gbps fiber transmission over 10-km single mode fiber under the operation conditions up to 70°C was also confirmed in 1.3-m wavelength.