diff --git a/String/Upper.js b/String/Upper.js
new file mode 100644
index 0000000000..d9aaceae3a
--- /dev/null
+++ b/String/Upper.js
@@ -0,0 +1,28 @@
+/**
+ * @function upper
+ * @description Will convert the entire string to uppercase letters.
+ * @param {String} url - The input URL string
+ * @return {String} Uppercase string
+ * @example upper("hello") => HELLO
+ * @example upper("He_llo") => HE_LLO
+ */
+
+const upper = (str) => {
+  if (typeof str !== 'string') {
+    throw new TypeError('Invalid Input Type')
+  }
+
+  let upperString = ''
+
+  for (const char of str) {
+    let asciiCode = char.charCodeAt(0)
+    if (asciiCode >= 97 && asciiCode <= 122) {
+      asciiCode -= 32
+    }
+    upperString += String.fromCharCode(asciiCode)
+  }
+
+  return upperString
+}
+
+export { upper }
diff --git a/String/test/Upper.test.js b/String/test/Upper.test.js
new file mode 100644
index 0000000000..81d605220e
--- /dev/null
+++ b/String/test/Upper.test.js
@@ -0,0 +1,9 @@
+import { upper } from '../Upper'
+
+describe('Upper', () => {
+  it('return uppercase strings', () => {
+    expect(upper('hello')).toBe('HELLO')
+    expect(upper('WORLD')).toBe('WORLD')
+    expect(upper('hello_WORLD')).toBe('HELLO_WORLD')
+  })
+})