In this paper new algorithms and procedures are reported which enable miniaturization and optimization of the thickness of a diaphragm for an all-glass extrinsic Fabry-Perot interferometer (EFPI)-based pressure sensor. Diaphragm etching improves the EFPI sensors ability to detect relatively small changes in pressure (0.1mmHg) and the resulting sensor exhibits excellent stability over time (drift < 1 mmHg / hour) for measurement in air and liquid. The diaphragm etching procedure involves fiber polishing followed by etching in hydrofluoric (HF) acid. An additional Ion-beam etching technique was investigated separately to compare with the HF-etching technique. A sensitivity better than 10 10 nm/kPa, which provides a pressure resolution of 0.05mmHg, is achieved by reducing the EFPI diaphragm thickness down to less than 2μm for the miniature pressure sensor used in this investigation (overall diameter of 200μm). The techniques reported is also applicable for the fabrication of high sensitivity sensors using a smaller fiber diameter e.g. 80μm.