IN THIS STUDY, FOR THE FIRST TIME, WE INTRODUCE A SIMPLE AND LOW COST PH SENSOR BASED ON A COMMERCIAL FIELD EFFECT Transistor (FET). THE Transistor WAS MECHANICALLY TREATED, ISOLATED AND USED AS AN ION SENSITIVE FIELD EFFECT Transistor (ISFET) [1] FOR PH DETECTION, AFTER ELECTRODEPOSITION OF THE SENSING MEMBRANE ON ITS SURFACE. POLYPYRROLE, AS A SUITABLE SENSING MEMBRANE, WAS ELECTRODEPOSITED ON THE OF Transistor FROM A SOLUTION CONTAINING PYRROLE MONOMER, HYDROQUINONE MONOSULFONATE [2] AS A PROPER LIGAND AND SODIUM SALICYLATE FOR AVOIDING THE SUBSTRATE OXIDATION, UNDER A TWO-STEP DEPOSITION CONDITIONS. THE PREPARED SENSOR SHOWED A NEAR-NERNSTIAN RESPONSE OF 52.3 MV PH-1 OVER A LINEAR PH RANGE OF 2.75-12.20, AN ULTRA LOW HYSTERESIS OF 0.56 MV, A VERY LOW DRIFT OF 0.14 MV H-1 AND A LOW RESPONSE TIME OF LESS THAN 8 S.