Photonic-crystal surface-emitting lasers (PCSELs) are considered as next-generation semiconductor lasers because they can operate in a high-power single mode. However, these devices are not suitable for low-threshold high-speed operation because they often require a long cavity length to achieve low loss. In this paper, we break this limit and demonstrate very low-threshold operation of the PCSELs for their high-speed application, using a triple-lattice photonic-crystal structure with 100 μm cavity length. A low threshold current of 29 mA at 10 ℃ and 36 mA at 25 ℃ under continuous wave (CW) operation were realized, which is comparable to the traditional high-speed distributed feedback Bragg (DFB) edge-emitting lasers. The far-field divergence angles defined by 1/e2 power were respectively 3.84°and 1.63°along the x- and y-directions. A small-signal modulation bandwidth of 5.8 GHz was obtained. By further optimizing the mesa size, the threshold current was decreased to 12 mA, which, to the best of our knowledge, is the lowest threshold current reported for PCSELs so far.