We report on the generation of continuous-wave (cw) ultraviolet (UV) laser light at λ=278nm by optical frequency doubling of visible light in β-BaB2O4 waveguides. Ridge-type waveguides were produced by He+ implantation, photolithography masking, and plasma etching. The final waveguides have core dimension of a few μm2 and show transmission losses of 5dB∕cm at 532nm and less than 10dB∕cm at 266nm. In our first experiments, a second harmonic power of 24μW has been generated at 278nm in an 8mm long waveguide pumped by 153mW at 556nm.