NOx sensing properties of were investigated by varying the sintering temperature in an effort to study the effects of the neck-width on gas sensitivity. sintered at , which exhibits neck-controlled conduction provides highest sensitivity of 47 and 29 at to NO and , respectively. The samples sintered beyond show sintering temperature-independent gas sensitivity. This may be because the grain boundary control is dominant at lower sintering temperatures and open neck control is dominant at higher sintering temperatures than . The NOx sensing mechanism of was briefly discussed.