Due to their growing power and shrinking size, thermal management and analysis have become one of the most critical concerns for power devices. Though finite element (FE) method is commonly employed in thermal analysis now, the uncertainty of material properties and the redundancy of repeat modeling still nag analyzers. In this paper, a simplified approach for steady thermal analysis of chips with variable power is proposed. Based on spatial autocorrelation and undetermined method, the steady temperature distribution could be directly determined with power distribution and example temperature measurement result, without identifying environment factors or material properties. The theory of the simplified approach is introduced at first in this paper. The characteristics of the simplified approach are discussed afterwards. Eventually, a case study is given to illustrate the procedure, of which the analytical result coincides with the actual measurement well.