pad 142 are not shown in fig1 an ammeter 150 may be disposed between the first electrode pad 122 and the second electrode pad 142 to measure a current therebetween the operation principle of the chemical sensor 100 according to example embodiments will now be described when a compound is in contact with the chemical sensor 100 the compound may be adsorbed by the sensing member 130 of the chemical sensor 100 in the sensing member 130 contacts for example a nano contact array in which the first nanowires 120 and the second nanowires 140 cross each other may be formed the resistance of the sensing member 130 to which the compound is adsorbed may be changed and the change of the resistance may be detected with a current difference a read voltage is applied to the first electrode pad 122 and the second electrode pad 142 and the correct difference is measured from the ammeter 150 the read voltage may be in the range of several mv to 10v dc according to the sensing member 130 and the chemical sensor 100 when the current difference is detected the concentration of the corresponding compound may be measured from the current difference in the chemical sensor 100 according to.