Organic semiconductors that function in field-effect transistors are further modified so that they will produce electronic signals in the presence of vapors related to nerve agents (phosphonate esters) and explosives (nitroaromatics). They are blended with compatible compounds that bind to these vapors, such as hydrogen bonding and Lewis acidic groups for the phosphonates and electron pi-donors for the nitroaromatics. They are also deposited as ultrathin films just a few monolayers in height. Transistors exposed to these vapors show changed currents when the vapors are present at less than part per million levels. They are much more sensitive to target vapors than they are to humidity. Arrays of these sensors will be designed so that their cumulative responses will be characteristic of a particular vapor of interest.