The fourth industrial revolution is the integration of new digital industrial technologies aimed at connecting and enabling interaction between humans, machines, and components, transforming production systems into fully automated and integrated equipment that communicate with each other. In this paper, we propose a new maturity model for Industry 4.0 (I4.0) startups using the combined compromise solution (CoCoSo) decision-making algorithm. This model assists companies seeking to transition their business towards I4.0 and can serve as a guiding procedure for systems on their path to full I4.0 implementation. First, we compile a list of key I4.0 dimensions from the literature and previous studies. Then, we gather opinions from industrial and academic experts to select the most relevant and important indicators for analyzing the maturity level of startups. We use the CoCoSo decision-making algorithm to prioritize the I4.0 dimensions and design the model elements. Three main sustainability dimensions are used as decision criteria with equal weight when prioritizing the I4.0 sub-dimensions. To evaluate the applicability of the model, we assess three Iranian startups operating at the Science and Technology Park using the proposed model and present the radar graph of their maturity level in each dimension. The proposed model can be readily used by startups to assess themselves, identify their strengths and weaknesses, better define improvement projects, and allocate their resources. To our knowledge, there is no similar assessment model in the literature that can be used by startups due to their innovative nature.