A device (102) for defining a pattern, for use in a particle-beam exposure apparatus (100), said device adapted to be irradiated with a beam (lb,pb) of electrically charged particles and let pass the beam only through a plurality of apertures, comprises an aperture array means (203) and a blanking means (202). The aperture array means (203) has a plurality of apertures (21,230) of identical shape defining the shape of beamlets (bm). The blanking means (202) serves to switch off the passage of selected beamlets; it has a plurality of openings (220), each corresponding to a respective aperture (230) of the aperture array means (203) and being provided with a deflection means (221) controllable to deflect particles radiated through the opening off their path (p1) to an absorbing surface within said exposure apparatus (100). The apertures (21) are arranged on the blanking and aperture array means (202,203) within a pattern definition field (pf) being composed of a plurality of staggered lines (p1) of apertures. Each of the lines (p1) comprises alternately first segments (sf) which are free of apertures and second segments (af) which each comprise a number of apertures spaced apart by a row offset (pm), said row offset being a multiple of the width (w) of apertures, the length (A) of said first segments (sf) being greater than the row offset. In front of the blanking means (202) as seen in the direction of the particle beam, a cover means (201) is provided having a plurality of openings (210), each corresponding to a respective opening (230) of the blanking means and having a width (w1) which is smaller than the width (w2) of the openings (220) of the blanking array means.