The mechanical stress distribution around the trench isolation of bipolar devices was evaluated in the cross-sectional plane, both by a two-dimensional stress simulation and by two-dimensional Raman spectroscopy. The results obtained by the different methods agreed well quantitatively. It was confirmed that the stress value reaches a local maximum at the bottom of the trench structure, and this stress is sufficiently high to sometimes generate crystal defects. The electrical characteristics of an 850-diode-junction array isolated by trench isolation further support the simulated and measured distributions. It is concluded that stress simulation, in combination with Raman spectroscopy measurements, is a very important tool for analyzing mechanical stress around the trench, and thus for improving isolation structures.