Sensitivity outside the electrodes of a quartz crystal microbalance (QCM) is typically 5%-10% of the total sensitivity for the popular planar AT-cut type, and can be a problem in many types of adsorption measurement. This off-electrode sensitivity has sometimes been assumed incorrectly to be due mainly to the electric "fringing field" at the electrode edge, despite the fact that no quantitative theory has been put forward as to how the fringing field could lead to off-electrode sensitivity. Tn fact, off-electrode sensitivity results from the mass distribution of the electrodes, and is virtually independent of the electric field. Recognition of this fact leads directly to a new QCM design which virtually eliminates the problem altogether; in the new design sensitivity outside the electrode covered area has been reduced from 6% to about 0.3%. Equations previously derived to predict the differential mass sensitivity of existing planar AT-cut QCM sensors are applied to the new design, and compared to experimental calibration measurements obtained using the ink-dot method. Agreement with theory is excellent.