Recently, the Alliance for Open Media (AOMedia) has initiated activities on exploring new coding tools with capabilities beyond AOMedia Video 1 (AV1). Among various coding modules within the conventional hybrid video coding structure, the block partitioning scheme builds the foundation of the codec and the related design needs to be sought out from the beginning. In this paper, a Semi-Decoupled Partitioning (SDP) method is proposed for coding block partitioning. With SDP, luma and chroma share the same coding block partitioning toward a specified partitioning depth. After this specified depth, the partitioning patterns of luma and chroma components can be optimized and signaled independently. The benefit of SDP is the additional flexibility of switching between dependent and independent partitioning patterns for luma and chroma since the characteristics of these color components can largely differ. The proposed method has been integrated on top of libaom research branch, and experimental results show that, significant coding gain can be achieved comparing to the libaom research anchor.