The molecular‐beam epitaxy (MBE) method is an important tool which can provide new and different types of semiconductor films. The effusion ovens used in MBE studies were not an ideal Knudsen‐type design that had employed small orifices. We have measured the beam intensity distribution of an effusion oven that had 240 small channels. Applying the theory of Clausing, who derived the angular distribution from a small hole of radiusrand lengthL, and using the superposition principle, we have compared the calculation with experimental data and found good agreement. Intensity distributions from an oven with a single large opening are also measured. This geometry cannot be calculated but actually provides a useful method of collimating molecular beams.