The Software Product Line (SPL) approach receives more attention due to the observed benefits, such as cost reduction, quality improvements, and reduced delivery time. Although organizations are aware of its potential benefits, they face some challenges while creating a clear road map to adopt this approach. Capability maturity models are developed to guide organizations by providing an extensive road map for improvement. Accordingly, we developed a capability maturity model, entitled SPL Capability Maturity Model (SPL‐CMM), to improve an organization's SPL capabilities by enabling the assessment of SPL‐specific processes and providing a guideline for process improvement. SPL‐CMM, developed based on SPICE‐ISO/IEC 330xx standard, has two dimensions of process and capability. The process dimension consists of 16 SPL‐specific processes defined under four process areas: business, architecture, technical, and organization, and the capability dimension has six capability and maturity levels from levels 0 to 5. It is a structured approach assisted by adequate measures with guidance on actions for improvement. A case study was conducted to check the applicability and usefulness of the proposed approach in a software company. The case study results show that SPL‐CMM is applicable for identifying the current state of the SPL process capability and the gaps for process improvement to the next level.