Determining single-escape (SE), double-escape (DE), and full-energy (FE) peak efficiencies is helpful in prompt gamma-ray neutron activation analysis, in which identifying complicated gamma peaks as well as quantifying spectra is crucial. The FE peak efficiency was measured at the National Institute of Standards and Technology for a closed-end, n-type high-purity germanium (HPGe) cylindrical detector using standard point sources, whereas SE and DE peak efficiencies and the SE-to-DE peak ratio for the HPGe detector were calculated using compact analytical expressions.