© 2015 The Electrochemical Society. The formation of sub-surface truncated tetrahedral voids beneath suspended ~40 nm thick dense InP shelves is achievable via a twostep etching method. The first step involves the electrochemical anodisation of n-type InP in aqueous KOH electrolyte resulting in the formation of truncated tetrahedral domains of pores beneath an ~40 nm thick dense surface layer with an individual pit that penetrates the dense surface layer of each domain. The second step involves the preferential chemical etching of these porous domains with only limited etching of the surrounding bulk InP and dense surface layer. The resulting structure of each domain is a truncated tetrahedral void with a dense InP layer suspended above it. This new technique may be a very useful tool in the fabrication of devices based on III-V semiconductors and it may be possible to extend the technique to the fabrication of free-standing InP nanofilms.