Boundary layer flow imaging can provide real time information for flight control of air vehicles, and collision avoidance and stealth detection of underwater vehicles. High density, micro-scaled sensor arrays based on microfabrication techniques have made it possible to enable these new applications. We report on the development of such a flow sensor array. It is realized by combining surface micromachining and three-dimensional assembly. It consists of a linear array of 16 integrated hot-wire anemometers (HWA) evenly spaced 1 mm apart. Each sensor uses a 400 μm long thermal element (hot-wire) that is made of a thin film nickel/polyimide composite, and is elevated 600 μm above the substrate. Under constant temperature (CT) mode, the threshold velocity sensitivity to water flow is down to 100 μm/s, and the frequency response to dynamic signals is up to 1000 Hz. The capabilities of the sensor array on boundary flow measurement and hydrodynamic wake imaging are demonstrated via wind tunnel and water channel experiments.