The invention discloses a Ka frequency-band solid-state power amplifier, which relates to an uplink channel transmission device in the field of satellite communication. The solid-state power amplifier comprises a level control unit, a driving amplifier, a solid-state power amplification module, an output coupler, a wave detector, a monitoring unit, a temperature sensor, a module power supply, and the like. The invention relates to an intra-waveguide space 12-route power combining technique, and a three-route waveguide power splitter and a three-route power combiner for waveguide branch lines are designed; four power single-chips are assembled on a four-route power combiner consisting of the waveguide branch lines, waveguide T-shaped nodes, and waveguide-microstrip probes in a transitional manner; and three four-route power combining modules subjected to special testing, together with a three-route power splitter and a four-route power combiner, from a 12-route power combining module. The power amplifier disclosed by the invention has the characteristics of compact structure, high integration degree, stable and reliable performance, light weight, low power consumption, and wide operating temperature range; and the power amplifier is especially applicable to the power amplification services of satellite communication microwave channels.