Remove the stems from the jalapeños, and halve them lengthwise. For a spicier syrup, keep the seeds and membrane intact; otherwise, remove the seeds and membrane.
In a pan, heat the water on high to a near boil and then add the sugar and stir continuously until the mix turns clear.
Add the jalapeño pepper halves,and bring the liquid to a quick boil.
Reduce the heat and simmer for 10 minutes. The sugar-water will begin to thicken and you may see it take on color from the chilies.
Remove the syrup from the heat. Let it cool for approximately 30 to 45 minutes or until it cools to room temperature.
Remove the jalapeño halves (and seeds if added).
Pour the syrup into an airtight container and let it chill for an hour in the refrigerator prior to use.
Keeping simple syrup refrigerated will prolong its shelf life to approximately one month. But for the best taste, use the simple syrup within two weeks of creation. The jalapeño can change the flavor when kept for prolonged periods.