The room temperature extraordinary magnetoresistance (EMR) of a mesoscopic sensor structure prepared from an InSb quantum well of dimension 30 nm wide/spl times/100 nm high/spl times/3 /spl mu/m long is reported. The observed EMR is 4.75% at a relevant field of 0.05 T. The advantages and disadvantages of this nonmagnetic composite semiconductor/metal structure relative to that of conventional magnetic giant magnetoresistance (GMR) and tunneling magnetoresistance (TMR) devices for use as read-heads in high-density magnetic recording are discussed.