Vines and other woody species growing in hot climates are commonly subjected to high temperature stress but just how high the temperatures have to get to be damaging remains uncertain. A hydrocooling system was adopted to control canopy temperatures over the growing season at 30, 35 and 40 °C and effects of temperature on growth, photosynthesis and net carbon budget of Vitis vinifera cv. Semillon vines assessed in field conditions. Shoot leaf area, biomass accumulation and photosynthesis were measured in selected shoots across the growing season. A carbon budget was determined from acquisition of carbon and sequestration of carbon as biomass. The temperature regimes affected shoot leaf growth, with largest canopies in the 35 °C vines and smallest in the 40 °C vines, with a two-fold difference. Leaf and stem biomass accumulations were unaffected but highest bunch biomass occurred with 30 °C vines and lowest with the 40 °C vines, a 30% difference. Rates of photosynthesis and nodes at which maximum rates occurred were enhanced by the temperatures. More carbon acquisition occurred in the 35 °C vines but more carbon was sequestered as biomass in 30 °C vines. Semillon grapevine photosynthesis and carbon budget had a high temperature threshold of 33 °C and long-term exposure to higher temperatures was detrimental to the performance.