Alignments and shape changes in [Formula Presented]Se

High-spin states in [Formula Presented]Se were studied using the [Formula Presented]Ge[Formula Presented],[Formula Presented] reaction at 40 MeV at the Florida State University Tandem-LINAC facility. Prompt [Formula Presented]-[Formula Presented] coincidences were observed using the Pitt-FSU detector array. The positive- and negative-parity yrast bands were extended up to spins of ([Formula Presented]) and ([Formula Presented]), respectively. Spin assignments were made based on directional correlation of oriented nuclei ratios whenever possible. A rich and complicated high-lying high-[Formula Presented] negative-parity structure was also found. The positive-parity yrast structure shows a change from large signature splitting at low spin to a more uniform level spacing at higher spins, as has been seen in the heavier [Formula Presented] isotones. Theoretically, this change is attributed to a shift from oblate to triaxial shape due to the alignment of a pair of [Formula Presented] protons.