The modulation and spectral properties of semi-insulating blocked planar buried heterostructure-distributed feedback lasers are described. The fabrication and performance are discussed. Typical threshold currents and differential quantum efficiencies for these lasers are 10-20 mA and 15-20%/facet, respectively. The room temperature output powers are approx. 20 mW. The lasers exhibit single-mode operation with a side-mode suppression ratio larger than 30 dB. The small-signal frequency response is shown. Calculation of the expected spectral broadening on the basis of a simulation of modulation at 16 Gb/s using a rate equation model agrees with the relatively small chirp observed experimentally.