This study investigates the R&D persistence with different external conditions based on US listed manufacturing firms for the period 2011-2019. Specifically, we analyze whether the fluctuation of R&D investment is related to short-term changes in sales, and how industrial technological intensity and competitive environment influence the relationship. We used the cost asymmetry model to identify the changes in R&D investment by sales behaviour. The results showed that the R&D investment of high-tech firms was stickier when sales declined as compared to low-tech firms. Therefore, R&D persistence tends to be strong in high-tech firms. In addition, R&D persistence was weakened by the competitive environment, and this finding was more pronounced for high-tech firms than for low-tech firms. This study has academic implications in the empirical analysis of the relationship between R&D persistence and external characteristics from a dynamic perspective.