InAs/InAs 1-xSb x strain-balanced superlattices (SLs) on GaSb are a viable alternative to the well-studied InAs/Ga 1-xIn xSb SLs for mid- and long-wavelength infrared (MWIR and LWIR) laser and photodetector applications, but the InAs/InAs 1-xSb x SLs are not as thoroughly investigated. Therefore, the valence band offset between InAs and InAs/InAs 1-xSb x, a critical parameter necessary to predict the SL bandgap, must be further examined to produce InAs/InAs 1-xSb x SLs for devices operational at MWIR and LWIR wavelengths. The effective bandgap energies of InAs/InAs 1-xSb x SLs with x = 0.28 - 0.40 are designed using a three-band envelope function approximation model. Multiple 0.5 μm-thick SL samples are grown by molecular beam epitaxy on GaSb substrates. Structural characterization using x-ray diffraction and atomic force microscopy reveals excellent crystalline properties with SL zero-order peak full-width-half-maximums between 30 and 40 arcsec and 20 x 20 μm2 area root-mean-square roughnesses of 1.6 - 2.7 A. Photoluminescence (PL) spectra of these samples cover 5 to 8 μm, and the band offset between InAs and InAs/InAs 1-xSb x is obtained by fitting the PL peaks to the calculated values. The bowing in the valence band is found to depend on the initial InAs/InSb valence band offset and changes linearly with x as C Ev-bowing= 1.58x - 0.62 eV when an InAs/InAs 1-xSb x bandgap bowing parameter of 0.67 eV is assumed. A fractional valence band offset, Q v = ΔE v/ΔE g, of 1.75 ± 0.03 is determined and is practically constant in the composition range studied.