Considering the problem of high failure rate and difficult maintenance of imported traveling wave tube amplifier, an indoor Ku-band 350 W solidstate power amplifier was developed. A novel 16-way power dividing/combining network was proposed, which was based on novel waveguide magic T, waveguide E-plane T-junction, coplanar magic T and half-height waveguide-to-microstrip probe transition. A Ku-band 450 W power amplifier module was achieved based on 16 pieces of 35 W gallium nitride power amplifier chips and the 16-way power dividing/combining network. Then, an indoor Ku-band 350 W solid-state power amplifier was successfully developed. The measured results show that the gain is greater than 73 dB, the output power is greater than 400 W between 13.75 GHz and 14.5 GHz. After calculation, the overall efficiency is 23.65% at rated power output, which is on par with international well-known companies. This power amplifier has excellent specifications and can replace imported TWTA products completely.