Glycolytic oscillations in cell extracts from aerobically grown yeast Saccharomyces carlsbergensis were recorded simultaneously via source drain currents of high electron mobility transistors (HEMTs) based on AlGaN/GaN heterostructures and by the fluorescence of NADH molecules. It is shown that the current signals are caused by the excitation light for the NADH fluorescence at 340 nm. This light induces photocurrent processes within the HEMTs. In the absence of any optical excitation the HEMTs show current oscillations with longer oscillation periods of 80–95 min, which are due to changes in the conductivity and/or the pH-value of the yeast extract in the dark.