We report a palm-top-size femtosecond diode-pumped mode-locked ${\text{Yb}}^{+3}:\text{KY}{\left({\text{WO}}_4\right)}_2$ solid-state laser with a semiconductor saturable absorber mirror utilizing soliton mode locking for shortening the cavity to 50 mm. An average output power of 680 mW and a pulse width of 162 fs were obtained at 1045 nm with a repetition rate of 2.8 GHz, which led to a peak power of 1.5 kW. Average power fluctuations of a modularized laser source were found to be ±10% for the free-running 3000 h operation and ±1% for the power-controlled 2000 h operation.