humidity control in domestic environments and for industrial purposes is the main cause of the increasing need for electrical humidity sensors [l, 21. The development of humidity sensing elements in thin-film form is dictated by on-chip in- tegration technology, which is the emerging technology in the area of sensor fabrication [3]. In a previous paper, the authors have proposed the use of MgAl,O, thin films as humidity sensors, with promising results [4]. This paper discusses the comparison between ax. and d.c. measurements of the humidity-sensitive elec- trical properties of MgA&O, thin Glms in order to obtain more detailed informations on their conduction mechanism. Experimental procednre The simple resistors used as the basic device for the sensors were prepared depositing on silica substrates thin tihn wires of chromium (200 nm thick). The elec- trodes, 100 pm wide and spaced 40 pm apart, were defined by a standard photolithographic process. Sen- sitive MgAl,O, thin films, about SO nm thick, were deposited on the electrodes by radiofrequency (r.f.) sputtering, using a sintered MgAl,O, target. The electrical response of thin Ghns was analysed by dc. and a.c. measurements at different relative humidity (r.h.) values. Electrical measurements were carried out in a suitable cell where both temperature and humidity were monitored. Monitor@ of r-h. was performed using a commercial sensor (Phys-them, mod. PCRC-II), which gave results accurate to within f2%. 1 V d.c. was applied to the thin tims by using a Keithley quasistatic CV-meter 595, for the period of time nec- essary to reach a steady-state value of the current, at room temperature and r.h. ranging from approximately 0 to 85%, in order to measure the charging current