A delivery device (1) for administering an active substance to a subject transdermal̂ comprises a first plate member (7) having a plurality of first chambers (8) formed therein. Solid form structures (2) comprising the active substance and of conical shape having a pointed skin penetrating tip (5) are located in the first chambers (8). A second plate member (12) having a plurality of second chambers (16) comprising a driving substance (18) is secured to the first plate member (7) with a first membrane (20) of an expandable material sealably located between the respective first and second plate members (7,12). Expansion of the driving substance (18) in the second chambers (22) urges the first membrane (20) into the corresponding first chambers (8) for in turn urging the solid form structures (2) to penetrate through a second membrane (22) into the skin of the subject. A third plate member (24) comprises a plurality of electrically powered heating elements (28) aligned with the second chambers (22) for heating the driving substance (18) in the second chambers (16) for in turn expanding the driving substances (18) therein.
