We demonstrate a nano-buried-heterostructure photonic crystal laser exhibiting an ultralow threshold of 730 nA at telecom wavelengths. This breakthrough was achieved by reducing the doping-induced losses of the laser cavity, enabling the efficient miniaturization of the active region. The laser can be directly modulated at 3 GHz at an energy cost of 1 fJ/bit, and a comparison to longer lasers is given. To the best of our knowledge, this is the lowest threshold reported for any laser operating at room temperature, facilitating on-chip links with ultralow energy consumption.