This study investigates the impact of extreme temperature exposure on corporate bond financing costs in China. Using raster temperature data matched with the geographical locations of subsidiaries of listed firms over the period 2007-2022, this paper first estimates industry-level temperature sensitivities of corporate profitability by season and derives industry-quarter-specific extreme temperature thresholds. Based on these thresholds, it constructs a measure of firm-level extreme temperature exposure, defined as the annual number of days on which local temperatures exceed the corresponding threshold, and examines its effect on bond issuance yields. The results show that: 1) Extreme temperatures exert widespread and significant effects on corporate profitability, with 59.7% of industries exhibiting statistically significant temperature sensitivity; 2) Greater extreme temperature exposure is associated with higher bond financing costs, an effect driven primarily by heat and negative temperature deviations, whereas cold and positive deviations show no significant impact; And 3) The adverse effect is more pronounced for non-state-owned enterprises, non-tradable goods enterprises, and labor-intensive firms. Mechanism analyses indicate that extreme temperature exposure impairs firm performance and elevates default risk, thereby raising financing costs. It further finds that strong environmental performance mitigates this adverse effect, while firms with higher reliance on external financing are more vulnerable to temperature shocks. These findings highlight climate physical risk as a financially material factor in corporate debt markets.