Sulfonic acid-based membrane gives the relatively high conductivity only in the presence of water, but phosphoric acid presents the relatively high proton conductivity without water because of its self dissociation natures to develop high temperature PEMFCs. We synthesized the thermostable material that has phosphorous groups based on poly(dimethyl siloxane) (PDMS). PDMS, which is intrinsically hydrophobic was modified to be amphiphilic by substituting end groups with hydrophilic phosphorous groups. Phase separation resulted in forming the proton conducting channels. The membranes maintained the constant proton conductivity above 130 degrees C under dry conditions. Also they were thermally stable up to 300 degrees C and may be used as high temperature proton conducting membrane at low humid conditions.