The conventional x-ray standing wave (XSW) technique [1, 2] is a phase sensitive and element specific Fourier technique, which is commonly used to analyse single crystals on the millimetre to centimetre scale. Here, we present an advanced microprobe technique based on the XSW method demonstrating that structural analysis can be achieved with chemical sensitivity on a microscopic scale. We apply the XSW microscopy technique to study the crystallographic polarity from inversion domains in GaN-based lateral polarity heterostructures. We focus the x-ray beam by a refractive lens [3] into a micrometre slice and generate the XSW field by Bragg-reflection from the (0002) diffraction planes recording the GaK_α fluorescence as a function of the incidence angle. In this first demonstration of microscopic polarity determination with x-rays, we analyse the reversion of polarity across a inversion domain boundary with a spatial resolution of 1.5 μm. The new micro-XSW technique will permit microscopic examinations of the crystalline structure of modern semiconductor devices with chemical sensitivity and structural resolution on the picometre scale.