Different types of phase separation in thick InGaN layers were studied using photoluminescence (PL) and x-ray diffraction (XRD). InGaN films of 100 nm in thickness were grown on 2 μm GaN templates with an In molar fraction ranging from 0% to 20% by metal organic chemical phase deposition (MOCVD). It is shown that suppression of the phase separation in InGaN can be made possible by increasing the TMIn flow rate, decreasing the layer thickness and decreasing the growth rate. Based on the results, two types of phase separation, microscopic quantum dots and macroscopic domains, are proposed accordingly. The influence of the growth conditions on each type is summarized respectively in this paper.