Semiconductor nanostructures are realized by patterning AlGaAs/GaAs heterostructures with an atomic force microscope. Steep potential walls, precise pattern transfer and a combination of in-plane and top gates can be achieved with this technique. The electronic properties of nanostructures defined in this way are discussed on two examples, namely a quantum point contact and a single electron transistor. For the quantum point contact we demonstrate quantized conductance at temperatures of 4 K and above. This indicates the strong confinement energy in this system. For the single electron transistor, the realization of special potential shapes and the observation of high-quality Coulomb blockade is shown.