[001]-oriented nanometer sized straight pores without branches were formed for the first time on (001) n-type InP surfaces by photoelectrochemical anodic reaction in HCl. The pore diameter, wall thickness and pore length could be changed in the ranges of 110-250 nm, 16-50 nm and 17-80 mm, respectively, by changing the anodizing overpotential and time. Based on the diffusion limited model for porous Si formation, the formation of [001]-aligned straight pores without branches on n-type InP was explained in terms of the short lifetime of holes combined with the presence of a strong electric held at the pore tip. Contrary to the expectation of blue-shifted photoluminescence (PL) emission due to quantum confinement at pore walls, porous (001) InP samples exhibited intense red-shifted PL peaks. This was explained by formation of a set of well defined new surface state levels on the anodized wall surfaces of pores.