In this work we report on the design, fabrication, electrical characterization and sensing tests of new silicon bipolar junction phototransistors, coated by Zn-(heptiloxy)-TPP. The finger-shaped emitter/base junction has been proved to enhance the responsivity in the blue spectral region with respect to the standard fully implanted detector (0.24A/W and 0.14A/W respectively at 5 V reverse bias). This effect has been experimentally tested in reverse biased E/B junction and, even though the phototransistor is operated with floating base, slightly forward biasing the E/B junction, this improvement in responsivity was still observed. The new transducers exhibit a beta current gain higher than 150 and were employed to detect ethanol concentrations down to 300ppm.