We present VUV observations of transitions between doubly excited sextet states in O3+, F4+ and Ne5+. Spectra were produced by collisions of an oxygen, uorine and neon beam with a nitrogen gas jet target. Prepared beam-gas experiment yields new and explicit information on doubly core-excited ions. Some observed lines were assigned to the 1s2s2p3 6S-1s2p33s, 3d 6P electric-dipole transitions in O3+, F4+ and Ne5+. Three lines have been reassigned. Present data are the first explicit measurements on transitions between sextet states in boronlike ions by beam-gas spectroscopy.