An inductive heating device (1) for heating an aerosol-forming substrate (20) comprising a susceptor (21) comprises: a device housing (10) a DC power source (11) for providing a DC supply voltage (VDC) and a DC current (IDC) a power supply electronics (13) comprising a DC/AC converter (132), the DC/AC converter (132) comprising an LC load network (1323) comprising a series connection of a capacitor (C2) and an inductor (L2) having an ohmic resistance (RCoil), a cavity (14) in the device housing (10) for accommodating a portion of the aerosol-forming substrate (20) to inductively couple the inductor (L2) of the LC load network (1323) to the susceptor (21). The power supply electronics (13) further comprises a microcontroller (131) to determine from the DC supply voltage (VDC) and the DC current (IDC) an apparent ohmic resistance (Ra), and from the apparent ohmic resistance (Ra) the temperature (T) of the susceptor (21).