The authors report on electromodulated intersubband ͑ISB͒ absorption experiments on AlN / GaN superlattices ͑SLs͒ grown on a transistorlike structure. A sample containing five SL periods shows two distinct absorption peaks related to ISB transitions in the SL and in the two dimensional electron gas located at the interface of the lowest SL barrier and the underlying GaN buffer. The ratio of those two absorption peaks can be adjusted by applying an external field, which influences the overall band structure and, more specifically, the free carrier density in the SL. This is a proof of concept of an on-off electro-optical modulator at 1.5 m.Intersubband ͑ISB͒ transitions in III-nitride based semiconductor superlattices ͑SLs͒ attract an increasing interest due to the large conduction band discontinuity and fast ISB relaxation time of this material system.1 Optimized plasmaassisted molecular-beam epitaxy ͑PAMBE͒ allows the synthesis of GaN quantum wells ͑QWs͒ with thicknesses in the range of 1 -2 nm, which yield ISB transitions in the commercially interesting telecommunication wavelength range 2,3 around 1.5 m. An attractive application for ISB devices in this spectral region is electro-optical modulators, for which coupled QWs ͑Ref. 4͒ are a classical approach. Unfortunately, coupled QW modulators using III nitrides and absorbing around 1.5 m require very thin barrier layers 5 and are thus extremely sensitive to thickness fluctuations on the monolayer ͑ϳ2.5 Å͒ scale. In addition, the strong ͑ϳ5 MeV/ cm͒ built-in piezo-and pyroelectric fields complicate the design. In this letter, we present an alternative solution for an electro-optical AlN / GaN modulator. It is based on the transfer of electrons between a regular SL and the two dimensional electron gas ͑2DEG͒ located in the triangular well at the interface between the lowest AlN barrier and the underlying GaN buffer.