  We report synthesis of single crystalline NaMnAs, confirm its
antiferromagnetic order and characterise the sample by photoemission
spectroscopy. The electronic structure was studied using optical transmittance,
x-ray and ultraviolet spectroscopy and by theoretical modeling using local
density approximation (LDA) extended to LDA+U when Heisenberg model parameters
were determined. Optical transmittance measurement have confirmed the
theoretical predictions that NaMnAs is a semiconductor. Also the N\'eel
temperature was closer determined for the first time from temperature
dependence of magnetization, in agreement with our Monte Carlo simulations.
