By the use of ceramic-to-metal high-vacuum sealing technology, a sealed-off, miniature, high-power nitrogen laser operating at 337.1 nm has been constructed. The laser is excited transversely by a fast Blumlein pulser and uses UV photoionisation stabilisation. Peak output powers exceed 150 kW with pulse lengths ranging from 0.3 to 1 ns. No deterioration of the output was observed over more than 10⁸ shots.